A refrigeration device has been proposed in which a liquid receiver is connected to the downstream side of a condenser, and liquid refrigerant collected by the liquid receiver is supplied to a compressor via a liquid injection circuit to lower the temperature of discharge refrigerant from the compressor (for example, see Patent Literature 1).
The technique described in Patent Literature 1 detects the temperature of discharge refrigerant from the compressor, and varies the opening degree of a flow control valve according to the detected temperature to control the injection flow rate.
In addition, heat pump air conditioners equipped with a four-way valve that switch between cooling and heating by reversing the flow of refrigerant have been variously proposed (for example, see Patent Literature 2).
In the technique described in Patent Literature 2, an injection pipe is connected between a compressor and a pipe connecting an indoor heat exchanger to an outdoor heat exchanger, thereby enabling liquid refrigerant flowing through the pipe to be supplied to the compressor.
Furthermore, an air-conditioning apparatus equipped with a plurality of solenoid valves and able to perform a cooling and heating mixed operation in addition to cooling and heating has been proposed (for example, see Patent Literature 3).
In the technique described in Patent Literature 3, for injection during heating, an expansion device is provided on an injection circuit to inject refrigerant at an intermediate pressure (hereinafter designated intermediate pressure refrigerant) into a compressor.
In this way, the technologies described in Patent Literature 1 to 3 inject liquid refrigerant into a compressor and lower the temperature of discharge refrigerant from the compressor in order to minimize damage to the compressor.